Influence of Co(CH3COO)2 concentration on thermal emissivity of coatings formed on titanium alloy by micro-arc oxidation

Ceramic thermal protection coatings on Ti6Al4V alloy were achieved by micro-arc oxidation (MAO) in the presence of Co(CH3COO)2. The morphology, crystallographic structure and chemical composition of the coating were characterized by various techniques. The thermal emission of the coating was measured by Fourier transform spectrometer apparatus. The bonding strength between the coating and substrate was studied, together with the thermal shock resistance of the coating. The results indicate that the content of Co in the coating layer significantly affects its thermal emissivity. Higher concentration of Co(CH3COO)2 in electrolytes leads to more Co ions into the coating, which enhances the emissivity of the coating. All the coatings show bonding strength higher than 10 MPa. In addition, the coating remains stable over 40 cycles of thermal shocking. The coating formed at 4 g/L Co(CH3COO)2 displays an average spectral emissivity value more than 0.9 and bonding strength about 10.4 MPa.

► High emissivity coating were fabricated by micro-arc oxidation (MAO).
► The spectral emission increased with increasing the concentration of Co(CH3COO)2.
► Bonding strength and thermal shock resistance were influenced by Co(CH3COO)2.
► Coatings possessed high emission and good bonding strength, thermal shock resistance.